…er the test

From the internal issue on the matter:

> When using the standard Jasmine version of it promises returned by the body function are automatically awaited. The Catalyst version of it is fake-async, so awaiting the promise does not make sense; however it would be nice if Catalyst automatically flushed the promise to replicate the experience of using standard it. This would allow users to do the following:

```
it('should fail later', async () => {
  await new Promise(r => setTimeout(r));
  fail('failure');
});
```
> In Catalyst today the above test will pass. If this proposal to automatically flush the resulting promise were implemented it would fail.

Flushing after the tests complete has been the default behavior inside
Google since 2020. Very few tests remain that use the old behavior of
only flushing microtasks. The example above would actually fail with
`fakeAsync` due to the pending timer, but the argument still remains the
same. We might as well just flush if we're going to fail the test
anyways by throwing if there's no flush at the end.